I removed the wall around the tub as part of a remodel. The old wall was plaster. I am putting up cement board. The tub has a radiused lip that goes against the wall. (The tub is about 1/4" away from the wall already). The old plaster wall came down over the lip. The new board would have to come out enough to clear the lip (about 1/4") as well as get past the gap between the tub and the wall (another 1/4"). Obviously, this was easier to fudge when the plaster was put up. How can I account for this now?